1. Field of the Invention
The present invention relates to an Fe-based amorphous alloy thin strip used for iron core materials in power transformers, high-frequency transformers and the like.
2. Description of the Related Art
Amorphous alloy thin strips are obtained by quenching alloys from their molten state. Known methods for manufacturing thin strips include centrifugal quenching, the single-roll method and the twin-roll method. These methods produce thin strips or wires by ejecting a molten metal from an orifice onto the inner or outer perimeter side of a metal drum rotating at high-speed to thus rapidly solidify the molten metal. Amorphous alloy thin strips with excellent electromagnetic properties, mechanical properties or corrosion resistance can also be obtained by appropriately selecting the alloy composition.
Because of these excellent properties, such amorphous alloy thin strips are promising as industrial materials for a wide variety of uses. Among them, Fe-based amorphous alloy thin strips, such as Fexe2x80x94Sixe2x80x94B ternary alloy, etc., are being employed as iron core materials for power transformers and high frequency transformers because of their low iron loss and high saturation magnetic flux density and magnetic permeability.
Amorphous alloy thin strips with insulating coatings are the most often proposed alternatives aimed at improving the electromagnetic properties of iron core materials. Insulating coatings have the effect of increasing interlayer insulating properties and reducing eddy current loss produced by cross-over flux, in transformer magnetic cores fabricated by layering coiled amorphous alloy thin strips. The following method has been disclosed in the prior art as a means of increasing interlayer insulation in Fe-based amorphous alloy thin strips used for iron core materials. This method (Japanese Unexamined Patent Publication No. 6-346219) increases interlayer insulation and improves magnetic permeability when a toroidal core is made, by introducing oxygen at 20% or less during the heat treatment step for the thin strip to form an oxide film-on the thin strip surface at from a few tens of nanometers to 100 nm; however, the resulting oxide layer thickness is too large and a sufficient improvement in iron loss cannot be achieved.
On the other hand, the following method has also been disclosed for the purpose of imparting stress to thin strips to improve iron loss, etc. In this method (Japanese Unexamined Patent Publication No. 61-250162), heat treatment is carried out in a mixed atmosphere of an inert gas and oxygen in order to form an oxide film layer to a thickness of 20-300 nm on the thin strip surface to impart compressive stress in the direction parallel to the surface of the thin strip; however, the oxide layer is too thick and a sufficient improvement in iron loss cannot be achieved by this method.
Other methods have also been disclosed which focus on the oxides on the thin strip surface, aimed at obtaining other effects. According to one method (Japanese Unexamined Patent Publication No. 2-4913) involving annealing of an alumina insulating film-equipped iron-based amorphous alloy thin strip obtained by baking with an aqueous treatment solution composed mainly of a colloidal alumina hydrate, oxidation of B is avoided and crystallization of the thin strip surface is prevented by introducing oxygen into the annealing atmosphere to form an oxide film of Si on the thin strip surface, while another method (Japanese Unexamined Patent Publication No. 59-150081) forms an oxide of Ti, Zr, Cr, Al or Si or a nitride of Al or Si on an amorphous material surface by vapor deposition to a thickness of 10 nm -3.7 xcexcm, to improve the abrasion resistance.
Thus, while the prior art techniques give thin strips having oxide layers formed on the thin strip surfaces for the purpose of improving iron loss of the thin strips, the thickness of the oxide layers cannot be adequately controlled, and therefore adequate improvement in iron loss has not be achieved. Moreover, since the prior art techniques involve formation of oxide layers, they have required complicated surface treatment, etc.
It is an object of the present invention to provide a low iron-loss Fe-based amorphous alloy thin strip having an ultrathin oxide layer with a controlled thickness, and a low iron-loss Fe-based amorphous alloy thin strip with a segregated layer containing either or both P and S at the lower section of an ultrathin oxide layer with a controlled thickness.
It is another object of the invention to provide an Fe-based amorphous alloy thin strip fabricated with an ultrathin oxide layer in a controlled structure on the thin strip surface, wherein the ultrathin oxide layer is formed with a two-layer structure on the thin strip surface to reduce iron loss.
The gist of the invention is as follows.
(1) AnFe-based amorphous alloy thin strip characterized by being a quenched metal thin strip obtained by ejecting a molten metal onto a moving substrate through a casting nozzle with a slot-shaped opening and quenching it to solidity, and by having an ultrathin oxide layer with a thickness of from 5 nm to 20 nm on at least one surface of the thin strip.
(2) An Fe-based amorphous alloy thin strip characterized by being a quenched metal thin strip obtained by ejecting a molten metal onto a moving substrate through a casting nozzle with a slot-shaped opening and quenching it to solidity, by having an ultrathin oxide layer on at least one surface of the thin strip, and by having a segregated layer containing either or both P and S at the lower section of the oxide layer.
(3) An Fe-based amorphous alloy thin strip characterized by being a quenched metal thin strip obtained by ejecting a molten metal onto a moving substrate through a casting nozzle with a slot-shaped opening and quenching it to solidity and by having an ultrathin oxide layer on at least one surface of the thin strip, and in that the ultrathin oxide layer has a two-layer structure.
(4) An Fe-based amorphous alloy thin strip according to any one of (1), (2) or (3) above, characterized by having an ultrathin oxide layer on at least one surface of the thin strip, which is not in contact with the substrate.
(5) An Fe-based amorphous alloy thin strip according to either of (2) or (4) above, characterized in that the thickness of the segregated layer containing either or both P and S is 0.2 nm or greater.
(6) An Fe-based amorphous alloy thin strip according to either of (3) or (4) above, characterized in that the two layers of the ultrathin oxide layer with the two-layer structure are both amorphous oxide layers.
(7) An Fe-based amorphous alloy thin strip according to either of (3) or (4) above, characterized in that the first oxide layer on the outermost surface of the thin strip in the ultrathin oxide layer with the two-layer structure is a crystalline oxide and amorphous oxide mixed layer, and the second oxide layer between the first oxide layer and the amorphous mother phase is an amorphous oxide layer.
(8) An Fe-based amorphous alloy thin strip according to either of (3) or (4) above, characterized in that the first oxide layer on the outermost surface of the thin strip in the ultrathin oxide layer with the two-layer structure is a crystalline oxide layer, and the second oxide layer between the first oxide layer and the amorphous mother phase is an amorphous oxide layer.
(9) An Fe-based amorphous alloy.thin strip according to any one of (1), (2), (3), (4), (5), (6), (7) or (8) above, characterized in that the ultrathin oxide layer has a composition which is Fe-based, Si-based, B-based or a composite thereof.
(10) An Fe-based amorphous alloy thin strip according to any one of (7), (8) or (9) above, characterized in that the crystalline oxide composing the ultrathin oxide layer is an Fe-based oxide with a spinel structure.
(11) An Fe-based amorphous alloy thin strip according to any:one of (3), (4), (6), (7), (8), (9) or (10) above, characterized in that the total thickness of the ultrathin oxide layer with the two-layer structure is from 5 nm to 20 nm, the thickness of the first oxide layer on the uppermost surface of the thin strip is from 3 nm to 15 nm, and the thickness of the second oxide layer between the first oxide layer and the amorphous mother phase is from 2 nm to 10 nm.
(12) An Fe-based amorphous alloy thin strip according to any one of (3), (4), (6), (7), (8), (9) or (10) above, characterized in that at least one element from among P, As, Sb, Bi, S, Se and Te is segregated in the second oxide layer.
(13) An Fe-based amorphous alloy thin strip according to (12) above, characterized in that at least one element from among P, As, Sb, Bi, S, Se and Te is present in the thin strip at a total content of from 0.0003% to 0.15% by weight.
(14) An Fe-based amorphous alloy thin strip according to any one of (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (12) or (13) above, characterized in that the sheet thickness of the thin strip is from 10 xcexcm to 100 xcexcm.